Add LZ4 support to initramfs-tools

[Benjamin Tegge]

Original Bug Text
=================

I found that I could enable LZ4 compression for initramfs on my vivid machine by installing liblz4-tool package, adding one line to mkinitramfs and installing a kernel compiled with CONFIG_CRYPTO_LZ4=y.

Please include support for (legacy) LZ4.

Attached patch includes changes made to the latest version (initramfs-tools_0.120ubuntu3).

[Julian Andres Klode (juliank)]

Should we use zstd instead? Compression time is about the same as lz4, but size is much smaller (49MB instead of 75MB for me). Not sure about decompression support.

[Benjamin Tegge (livewirebt)]

I haven't done any benchmark comparisons between the two but zstd would be great.

Thumbs up on the work you and others are doing to implement zstd into packaging.

[Julian Andres Klode (juliank)]

Apparently the kernel does not yet support zstd for initramfs, but it would be nice if it did.

[Balint Reczey (rbalint)]

I plan uploading the attached fix in the next days after discussing this a bit on ubuntu-devel.

[Balint Reczey (rbalint)]

Initramfs-tools-core should also suggest liblz4-tool package.

[Steve Langasek (vorlon)]

This is a low-priority bug and has missed the window for 18.04. I'm nack'ing this for FFe.

The original request remains valid, so I'm resetting this to a non-FFe bug rather than closing it.

[Balint Reczey (rbalint)]

The fix was picked by Debian and is included in Ubuntu starting with 131ubuntu1 in Cosmic.

[Dimitri John Ledkov (xnox)]

Ubuntu core devices forced set LZMA which is now unsupported, fixing to use LZ4 on these now as well.

[Paul Menzel (paulmenzel)]

Can this be closed/tagged as fixed?